1. Field of the Invention
The present invention relates in general to a power supply for both alternating current (AC) and direct current (DC), and more particularly to a power supply for both AC and DC which is capable of selectively inputting AC and DC voltages from external power sources and converting the inputted voltages into a DC voltage appropriate to an associated device.
2. Description of the Prior Art
Portable small-sized power supplies, which are typically called adapters, are adapted for converting or transforming input voltages into voltages necessary to drive associated devices. Examples of such conventional portable small-sized power supplies are shown in FIGS. 1a to 1c herein.
FIG. 1a is a block diagram showing the construction of a conventional AC/DC power supply. As shown in this drawing, the conventional AC/DC power supply comprises a line filter 11 for attenuating electromagnetic noise contained in an AC input voltage, a transformer 12 for transforming a filtered AC signal from the line filter 11 into a voltage appropriate to an associated device, a controller 13 for controlling an output voltage of the power supply in response to a voltage fed from a secondary coil of the transformer 12 back thereto, and a rectifier 14 for rectifying a transformed AC signal from the transformer 12 into a DC signal and outputting the rectified DC signal as a drive voltage to the associated device.
In the above-mentioned conventional AC/DC power supply, the controller 13 controls the output voltage by adjusting a pulse duration of a pulse width modulation (PWM) signal in a trimmer manner or by setting the number of turns of the secondary coil of the transformer 12 to different values by regions in order to raise efficiency. However, this control method increases the volume and weight of the power supply, thereby making it inconvenient for a user to carry the power supply.
FIG. 1b is a block diagram showing the construction of a conventional DC/DC power supply. As shown in this drawing, the conventional DC/DC power supply comprises a line filter 21 for attenuating electromagnetic noise contained in a DC input voltage, a transformer 22 for transforming a filtered DC signal from the line filter 21 into a voltage appropriate to an associated device, and a controller 23 for controlling an output voltage of the power supply in response to a voltage fed from a secondary coil of the transformer 22 back thereto.
The above-mentioned DC/DC power supply is convenient to carry owing to its small size, but is disadvantageous in that a user has the trouble of having to carry it together with an AC/DC power supply while in motion for a lengthy period of time.
In order to solve the above problems with the conventional AC/DC power supply and DC/DC power supply, there has been proposed a power supply for both AC and DC having an AC/DC converter and DC/AC converter integral with each other, which power supply is disclosed in Korean Utility Model Laid-open Publication No. 1999-15641 and shown in FIG. 1c herein.
The proposed power supply comprises a constant-voltage circuit for maintaining a DC input voltage constant, a first filter for attenuating electromagnetic noise contained in the DC input voltage, a DC/DC converter integrated circuit (IC) for controlling the operation of a transistor in response to an output voltage of the transistor fed back thereto, a second filter for attenuating electromagnetic noise contained in an AC input voltage, a first rectifier for rectifying a filtered AC signal from the second filter into a DC signal, and a PWM control IC for driving a field effect transistor (FET) in a main switch to induce energy in a transformer. The switch acts to perform a switching operation to induce the energy in the transformer. The power supply further comprises a second rectifier for rectifying a voltage induced in a secondary coil of the transformer, and an error amplifier for, when overcurrent is generated in the secondary coil of the transformer, feeding the generated overcurrent back to the PWM control IC to drop the voltage induced in the secondary coil of the transformer so as to protect the power supply and associated circuitry from the overcurrent.
However, in the case where the proposed power supply is applied to large-capacity portable equipment, such as a notebook computer, to supply power thereto, it must be constructed with a heavy weight and large volume, resulting in an increase in manufacturing cost. Further, it is very inconvenient to use within transportation means, such as an airplane, vehicle, vessel and the like.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a power supply for both alternating current (AC) and direct current (DC) which has an AC/DC converter and DC/DC converter detachably coupled with each other.
It is another object of the present invention to provide a power supply for both AC and DC which is capable of selecting a level of an output DC voltage.
In accordance with the present invention, the above and other objects can be accomplished by the provision of a power supply for both alternating current (AC) and direct current (DC), comprising an AC/DC converter including a first line filter for attenuating electromagnetic noise contained in an AC input voltage, a rectifier for converting a filtered AC signal from the first line filter into a DC signal, a transformer for transforming the DC signal converted by the rectifier into a desired DC voltage, and a first pulse width modulation (PWM) controller for controlling an operation of the transformer; and a DC/DC converter detachably coupled with the AC/DC converter, the DC/DC converter including a second line filter for inputting the DC voltage from the AC/DC converter or an external DC voltage and attenuating electromagnetic noise contained in the inputted DC voltage, a drive voltage output unit for converting a filtered DC signal from the second line filter into a drive voltage to drive an associated device, a second PWM controller for controlling an operation of the drive voltage output unit, and an output voltage controller for controlling a voltage level of an output DC signal from the drive voltage output unit.
Preferably, the power supply may further comprise an output voltage selector connected to the DC/DC converter, the output voltage selector selecting a voltage level appropriate to the associated device and controlling an operation of an oscillator in the second PWM controller according to the selected voltage level so as to control the voltage level of the output DC signal from the drive voltage output unit.
More preferably, the output voltage controller may include a resistor array; and a multiplexer for selecting a resistance of the resistor array in response to a value selected by a dip switch in the output voltage selector and outputting a control signal based on the selected resistance to the oscillator in the second PWM controller to select the voltage level of the output DC signal from the drive voltage output unit.